The effect of distance on reaction time in aiming movements

Target distance affects movement duration in aiming tasks but its effect on reaction time (RT) is poorly documented. RT is a function of both preparation and initiation. Experiment 1 pre-cued movement (allowing advanced preparation) and found no influence of distance on RT. Thus, target distance does not affect initiation time. Experiment 2 removed pre-cue information and found that preparing a movement of increased distance lengthens RT. Experiment 3 explored movements to targets of cued size at non-cued distances and found size altered peak speed and movement duration but RT was influenced by distance alone. Thus, amplitude influences preparation time (for reasons other than altered duration) but not initiation time. We hypothesise that the RT distance effect might be due to the increased number of possible trajectories associated with further targets: a hypothesis that can be tested in future experiments

The effect of time constraint on anticipation, decision making, and option generation in complex and dynamic environments

Researchers interested in performance in complex and dynamic situations have focused on how individuals predict their opponent(s) potential courses of action (i.e., during assessment) and generate potential options about how to respond (i.e., during intervention). When generating predictive options, previous research supports the use of cognitive mechanisms that are consistent with long-term working memory (LTWM) theory (Ericsson and Kintsch in Phychol Rev 102(2):211–245, 1995; Ward et al. in J Cogn Eng Decis Mak 7:231–254, 2013). However, when generating options about how to respond, the extant research supports the use of the take-the-first (TTF) heuristic (Johnson and Raab in Organ Behav Hum Decis Process 91:215–229, 2003). While these models provide possible explanations about how options are generated in situ, often under time pressure, few researchers have tested the claims of these models experimentally by explicitly manipulating time pressure. The current research investigates the effect of time constraint on option-generation behavior during the assessment and intervention phases of decision making by employing a modified version of an established option-generation task in soccer. The results provide additional support for the use of LTWM mechanisms during assessment across both time conditions. During the intervention phase, option-generation behavior appeared consistent with TTF, but only in the non-time-constrained condition. Counter to our expectations, the implementation of time constraint resulted in a shift toward the use of LTWM-type mechanisms during the intervention phase. Modifications to the cognitive-process level descriptions of decision making during intervention are proposed, and implications for training during both phases of decision making are discussed

Searching for the Majority: Algorithms of Voluntary Control

Voluntary control of information processing is crucial to allocate resources and prioritize the processes that are most important under a given situation; the algorithms underlying such control, however, are often not clear. We investigated possible algorithms of control for the performance of the majority function, in which participants searched for and identified one of two alternative categories (left or right pointing arrows) as composing the majority in each stimulus set. We manipulated the amount (set size of 1, 3, and 5) and content (ratio of left and right pointing arrows within a set) of the inputs to test competing hypotheses regarding mental operations for information processing. Using a novel measure based on computational load, we found that reaction time was best predicted by a grouping search algorithm as compared to alternative algorithms (i.e., exhaustive or self-terminating search). The grouping search algorithm involves sampling and resampling of the inputs before a decision is reached. These findings highlight the importance of investigating the implications of voluntary control via algorithms of mental operations

Action Without Awareness: Reaching to an Object You Do Not Remember Seeing

BACKGROUND: Previous work by our group has shown that the scaling of reach trajectories to target size is independent of obligatory awareness of that target property and that "action without awareness" can persist for up to 2000 ms of visual delay. In the present investigation we sought to determine if the ability to scale reaching trajectories to target size following a delay is related to the pre-computing of movement parameters during initial stimulus presentation or the maintenance of a sensory (i.e., visual) representation for on-demand response parameterization. METHODOLOGY/PRINCIPAL FINDINGS: Participants completed immediate or delayed (i.e., 2000 ms) perceptual reports and reaching responses to different sized targets under non-masked and masked target conditions. For the reaching task, the limb associated with a trial (i.e., left or right) was not specified until the time of response cuing: a manipulation that prevented participants from pre-computing the effector-related parameters of their response. In terms of the immediate and delayed perceptual tasks, target size was accurately reported during non-masked trials; however, for masked trials only a chance level of accuracy was observed. For the immediate and delayed reaching tasks, movement time as well as other temporal kinematic measures (e.g., times to peak acceleration, velocity and deceleration) increased in relation to decreasing target size across non-masked and masked trials. CONCLUSIONS/SIGNIFICANCE: Our results demonstrate that speed-accuracy relations were observed regardless of whether participants were aware (i.e., non-masked trials) or unaware (i.e., masked trials) of target size. Moreover, the equivalent scaling of immediate and delayed reaches during masked trials indicates that a persistent sensory-based representation supports the unconscious and metrical scaling of memory-guided reaching

Uncertainty Compensation in Human Attention: Evidence from Response Times and Fixation Durations

BACKGROUND: Uncertainty and predictability have remained at the center of the study of human attention. Yet, studies have only examined whether response times (RT) or fixations were longer or shorter under levels of stimulus uncertainty. To date, no study has examined patterns of stimuli and responses through a unifying framework of uncertainty. METHODOLOGY/PRINCIPAL FINDINGS: We asked 29 college students to generate repeated responses to a continuous series of visual stimuli presented on a computer monitor. Subjects produced these responses by pressing on a keypad as soon a target was detected (regardless of position) while the durations of their visual fixations were recorded. We manipulated the level of stimulus uncertainty in space and time by changing the number of potential stimulus locations and time intervals between stimulus presentations. To allow the analyses to be conducted using uncertainty as common description of stimulus and response we calculated the entropy of the RT and fixation durations. We tested the hypothesis of uncertainty compensation across space and time by fitting the RT and fixation duration entropy values to a quadratic surface. The quadratic surface accounted for 80% of the variance in the entropy values of both RT and fixation durations. RT entropy increased as a function of spatial and temporal uncertainty of the stimulus, alongside a symmetric, compensatory decrease in the entropy of fixation durations as the level of spatial and temporal uncertainty of the stimuli was increased. CONCLUSIONS/SIGNIFICANCE: Our results demonstrate that greater uncertainty in the stimulus leads to greater uncertainty in the response, and that the effects of spatial and temporal uncertainties are compensatory. We also observed compensatory relationship across the entropies of fixation duration and RT, suggesting that a more predictable visual search strategy leads to more uncertain response patterns and vice versa

The SDF-1α/CXCR4 Axis is Required for Proliferation and Maturation of Human Fetal Pancreatic Endocrine Progenitor Cells

The chemokine receptor CXCR4 and ligand SDF-1α are expressed in fetal and adult mouse islets. Neutralization of CXCR4 has previously been shown to diminish ductal cell proliferation and increase apoptosis in the IFNγ transgenic mouse model in which the adult mouse pancreas displays islet regeneration. Here, we demonstrate that CXCR4 and SDF-1α are expressed in the human fetal pancreas and that during early gestation, CXCR4 colocalizes with neurogenin 3 (ngn3), a key transcription factor for endocrine specification in the pancreas. Treatment of islet like clusters (ICCs) derived from human fetal pancreas with SDF-1α resulted in increased proliferation of epithelial cells in ICCs without a concomitant increase in total insulin expression. Exposure of ICCs in vitro to AMD3100, a pharmacological inhibitor of CXCR4, did not alter expression of endocrine hormones insulin and glucagon, or the pancreatic endocrine transcription factors PDX1, Nkx6.1, Ngn3 and PAX4. However, a strong inhibition of β cell genesis was observed when in vitro AMD3100 treatment of ICCs was followed by two weeks of in vivo treatment with AMD3100 after ICC transplantation into mice. Analysis of the grafts for human C-peptide found that inhibition of CXCR4 activity profoundly inhibits islet development. Subsequently, a model pancreatic epithelial cell system (CFPAC-1) was employed to study the signals that regulate proliferation and apoptosis by the SDF-1α/CXCR4 axis. From a selected panel of inhibitors tested, both the PI 3-kinase and MAPK pathways were identified as critical regulators of CFPAC-1 proliferation. SDF-1α stimulated Akt phosphorylation, but failed to increase phosphorylation of Erk above the high basal levels observed. Taken together, these results indicate that SDF-1α/CXCR4 axis plays a critical regulatory role in the genesis of human islets

Expression and activity of the calcitonin receptor family in a sample of primary human high-grade gliomas

BACKGROUND: Glioblastoma (GBM) is the most common and aggressive type of primary brain cancer. With median survival of less than 15 months, identification and validation of new GBM therapeutic targets is of critical importance. RESULTS: In this study we tested expression and performed pharmacological characterization of the calcitonin receptor (CTR) as well as other members of the calcitonin family of receptors in high-grade glioma (HGG) cell lines derived from individual patient tumours, cultured in defined conditions. Previous immunohistochemical data demonstrated CTR expression in GBM biopsies and we were able to confirm CALCR (gene encoding CTR) expression. However, as assessed by cAMP accumulation assay, only one of the studied cell lines expressed functional CTR, while the other cell lines have functional CGRP (CLR/RAMP1) receptors. The only CTR-expressing cell line (SB2b) showed modest coupling to the cAMP pathway and no activation of other known CTR signaling pathways, including ERK1/2 and p38 MAP kinases, and Ca2+ mobilization, supportive of low cell surface receptor expression. Exome sequencing data failed to account for the discrepancy between functional data and expression on the cell lines that do not respond to calcitonin(s) with no deleterious non-synonymous polymorphisms detected, suggesting that other factors may be at play, such as alternative splicing or rapid constitutive receptor internalisation. CONCLUSIONS: This study shows that GPCR signaling can display significant variation depending on cellular system used, and effects seen in model recombinant cell lines or tumour cell lines are not always reproduced in a more physiologically relevant system and vice versa